If you add the pragma ScopedTypeVariables to your file, it works the way you would assume. However you will have to change the toplevel signature to iterateListF :: forall a. (a -> a) -> a -> Fix (ListF a) in order to make it work (added the forall a.).
Thanks, that worked. As far as I understand, the problem is because in this definition: where f :: a -> ListF a a f a = ConsF a (fn a) There's an implicit quantifier in type of `f`, like this: `f :: forall a. a -> ListF a a`. When I add `ScopedTypeVariables` and `forall a. ...` in top level definition, it's like all `a`s in scope of top level definition are same, except when explicitly defined as `forall a. ...`. Is my intuition correct? --- Ömer Sinan Ağacan http://osa1.net